1. Field of the Invention
The present invention relates to a control system suitable for control of an image forming apparatus having a plurality of objects to be controlled.
2. Description of the Prior Art
Function of OA equipment have been remarkably improved owing to the double effects of both the recent development of the semiconductor integrated circuit technology and the computer technology. However, the improvement of the functions of OA equipment causes the contents of various functions which are controlled to be complicated and highly advanced, so that a control amount extremely increases and the overhead to input into or output from each load also increases Thus, the more advanced control CPU having a larger bit capacity must be used. In association with this, a hardware constitution becomes complicated and enlarged in size and a software constitution also becomes complicated and advanced, resulting in an increase in product cost.
In addition, complication and enlargement of the hardware constitution increase the number of signal lines in equipment and cause the wirings of the signal lines to be increased and complicated As the control amount increases, the more the number of wirings increases. When the wiring bundles (harnesses) increase in number and size, they can be easily influenced by the induction noises from other signal lines and the equipment is enlarged in size. This enlargement is contrary to a requirement of the user for a reduction in size and weight of the equipment.
FIG. 1 shows an example of a constitution of a conventional copying machine, which is a middle-scale OA equipment.
This copying machine uses a total of six one-chip CPUs for control of each section of the machine, and each one-chip CPU integrally includes cheap ROM, RAM, I/0 control unit, and analog-to-digital (A/D) converter. As these one-chip CPUs, .mu.COM87AD made by Nippon Electric Co., Ltd. are used.
Objects to be controlled in the copying machine body 100 are distributingly controlled by four one-chip CPUs. A master CPU 110 mainly performs an operation display sequence control 111. A slave CPU-A 112 mainly performs a control 113 of a stepper motor and a developer. A slave CPU-B 114 mainly performs a control 115 of a DC servo motor in a PLL manner A slave CPU-C 116 mainly performs a control 117 of a potential of a photo sensitive material, erasing, and stabilization of a light amount of a halogen lamp for exposure.
On one hand, to control peripheral devices of the machine, a slave CPU-D 120 controls an auto document feeder (ADF) 121 A slave CPU-E 130 controls a sorter 131. Hitherto, those one-chip CPUs are mutually connected by a control bus consisting of a number of signal lines The ADF 121 and sorter 131 are merely connected to the peripheral devices of the machine, so that total six one-chip CPUs including the objects to be controlled of the copying machine body are used.
On the other hand, in the case where a number of sorters 131 are connected in series or where a paper deck (cassette for a large quantity of copy), a charge counter, an OMR, an OCR, etc. are further connected as accessory devices, the number of one-chip CPUs which are used increases in association with those extra devices. With such a system configuration, it is inevitable that the communications among the CPUs become complicated and connections of signals among the CPUs also become complicated. This tendency becomes conspicuous more and more with an increase in number of CPUs for control as the number of external devices which are connected increases.
To prevent this problem, a constant protocol is determined in communications among the CPUs and in the case where some information is sent to the specified slave CPU from the master CPU 110, address information and data information are time-sharingly sent through the bus. However, in this case, the overhead due to the program control is fairly enlarged. On one hand, upon reception as well, a program process must be carried out to decode the received data, so that it also takes a considerable long time for the decoding. As described above, the overhead due to transmission and reception increases, so that a conventional method is inadequate to a response which requires a high speed.
FIG. 2 shows a block arrangement in the case where a system constitution was increased. FIG. 3 shows an example of the arrangement of FIG. 2.
In the diagrams, the same parts and components as those in FIG. 1 are designated by the same reference numerals.
The sorter-I 131 corresponds to the sorter 131 in FIG. 1. A sorter-II 141 is the same as the sorter-I and connected in series A paper deck 151 and a charge counter 161 are also connected.
FIG. 2 shows an example in which the control elements are mutually connected by way of serial communication.
For this purpose, a constant protocol is determined in communication among the CPUs. In the case where some information is sent from the master CPU 110 to the specified slave CPU, the address information and data information are time-sharingly transmitted through the bus. However, the overhead due to the program control extremely increases. In addition, even in the case of reception as well, the program process must be carried out to decode the received data, so that it also takes a fairly long time for the decoding As mentioned above, since the overhead due to the transmission and reception increases, the method of FIG. 2 is improper for a response which requires a high speed.
Hitherto, for the serial communicating function included in a microcomputer, an internal interruption occurs upon transmission and reception and each time the interruption occurs, the CPU interrupts the task which is at present being executed and enters the interruption processing routine. Therefore, in the case where an external interruption or a plurality of interruptions due to communication are simultaneously inputted, the task which is at present being executed has to be interrupted for a long time and the influence due to the interruption cannot be ignored. Therefore, the program must be made in consideration of such a situation with religious care. Further, there is also a situation such that the process is interfered by such multi-interruptions and the control function is adversely influenced. Therefore, it is extremely difficult to change and extend the system configuration which has once been determined.
In addition, a malfunction of the whole apparatus occurs due to the influences of the long signal lines (cables) to connect the CPUs, the time lag of the transmission timing of a signal due to such long lines, and the induction noise due to other signal lines or external circumstances, resulting in a reduction in reliability of the apparatus, or the like.